This invention relates to non-return valves which allow high volume flow rates in a selected direction through a fluid passage but change to a non-return configuration at low reverse pressure differentials along the passage.
It is an aim of this invention to provide a relatively light non-return valve in which the discontinuity and functional losses of the flow through the valve are reduced compared to those found in conventional non-return valves, whilst maintaining a relatively high speed and effective shut off. It is a further aim of this invention to provide a non-return valve which can be positioned closely downstream of a fan, thereby assisting the design of compact equipment employing a fan in combination with a non-return valve.
According to this invention there is provided a non-return valve which comprises a relatively inflexible apertured valve body which supports the upstream end of valve closure means which is formed by a sleeve of flexible but impermeable sheet material, the valve body and sleeve together defining a fluid passage, and closure support means formed by a skeletal structure arranged within the fluid passage so that forward flow from the upstream end of the sleeve to the downstream end causes the sleeve to inflate and allow relatively unimpeded flow therethrough whilst reverse flow causes the sleeve substantially sealingly to collapse upon the skeletal structure.
Advantageously the sleeve includes a generally frusto-conical downstream portion, the diameter of the portion decreasing towards the downstream end and the included angle of the frusto-conical portion preferably lies in the range of from 6.degree. to 10.degree.. The ratio of the axial length of the sleeve to the maximum transverse dimension of the upstream end of the fluid passage is preferably not less than 0.8:1 and a ratio of 1.2:1 has been found to be particularly effective. The sleeve can conveniently be formed of a rubberised fabric material. The skeletal structure may be of generally frusto-conical form, the larger end of the structure lying upstream of the smaller end and adjacent the upstream end of the sleeve and the included angle of the skeletal structure is preferably not greater than 120.degree. to reduce the possibility of leakage paths forming when the valve is in its non-return mode. This invention also extends to an arrangement in which the valve body is the efflux duct of a fan.
One embodiment of a valve, according to the invention, is described by way of example with reference to the accompanying drawings in which: